What's the point of a log?

Aeolus

Aeolus

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What\'s the point of a log?

Sailing all the last summer without a working log, I've concluded that it doesn't really serve much useful purpose. GPS gives me a very accurate SOG from which, if I know what the tides are doing, I can estimate my speed thru the water. Sure, if GPS fails, then I'll be 'in the dark' but knowing SOG, especially in coastal waters, doesn't seem to me to be a significant safety issue.

So can anyone suggest a reason not to remove the log impeller and seal off the thru-hull?
 
Re: What\'s the point of a log?

Er,whats the point of a complicated ships electrical system and battery arrangement if you only use mechanical systems log/lead and placcy sextant and compass and yeoldepaperchart (and a self powered gps in a waterproof container of course !)
I take it you will not be replacing the failed electric log cos it is unreliable and expensive !
 
Re: What\'s the point of a log?

Our log doesn't work either - but a new impeller is only about £30 (NASA one) - so I'll be fixing it. Didn't really miss it this summer, but:

* Useful to note the difference between SOG and Log (this is the tide)
* When doing long passages the GPS in only turned on to take a fix (to save battery) and in between the log would be useful to show what speed is like.

Jonny
 
Re: What\'s the point of a log?

[ QUOTE ]
GPS gives me a very accurate SOG from which, if I know what the tides are doing, I can estimate my speed thru the water.

[/ QUOTE ]

0.5 kn of tide or current can make a real difference and I defy you to estimate boat speed to that accuracy. In an unfamiliar boat and rough sea, I would not be confident in my ability to estimate boat speed better than +/- 2Kn or worse. The combination of an accurate log and a GPS is a great tool IMHO.
 
Re: What\'s the point of a log?

I agree that I can't estimate boat speed very accurately, but cruising mostly in coastal waters, speed thru the water doesn't seem that important a piece of information. I'm not racing or trying to beat any speed records.

And I agree with Jonny that it is interesting but so are lots of other pieces of information for which I don't have instruments.

I'm really trying to find out if there are reasons why it would be a bad idea to remove the log and just depend on GPS.
 
Re: What\'s the point of a log?

I find comparing the SOG with boat speed very useful; ie seeing that you are working the tide to best advantage. Or not, as the case may be!
 
Re: What\'s the point of a log?

Ours broke years ago and i don't miss it. Can't really see any need for it now. SOG is all that matters here when the tide runs at 5kts.
 
Re: What\'s the point of a log?

You've really turned this one on its head, the idea of using a complex system to replace a simpler one is not one that has crossed my mind, but you're quite right that it is possible to do without.

Hmm, bucket-&-chuck-it plus GPS position/charted depth and tidal height to derive depth I think we should get rid of them all!

Steve
 
Re: What\'s the point of a log?

I know that more complex to replace simpler is counter-intuitive, but the GPS seems to be much more reliable. No damn shellfish growing in it.

Plus I can lose a thru-hull hole.
 
Re: What\'s the point of a log?

If your gps goes down, then you can't do DR without knowing how far you've been through the water. I carry a spare mechanical towed log as well as the through hull.

So gps goes down and there is a fog bank coming what are you going to do next? you can't navigate without it.
 
Re: What\'s the point of a log?

Mine worked last year but not accurately enough to be useful and has given up the ghost this year. I can't see the need either. SOG tells me if I'm going to make a tidal gate and if sail trimming is improving things. Fixed GPS and a hand-held and plenty of spare batteries seems adequate to me.
 
Re: What\'s the point of a log?

OK! I would not dream of telling you you should have a log -you will be perfectly OK without!

But it is important to me because I find it satisfying to, for example, find a 1kn counter current when fighting a 1kn tide. I haven't raced for years, but it makes a big difference to your arrival time in the pub and would be difficult without a log as well as a GPS.
 
Re: What\'s the point of a log?

In what circumstances do you anticipate that the GPS will go down?

This is not a "smart alec" question. It is a significant issue for proper risk analysis.
 
Re: What\'s the point of a log?

Possibly I'm over cautious as I've been off the Spanish coast in the winter trying to make a land fall when two hand helds and one fixed went down within 12 hours.

The two hand helds were virtually unused as they had always been back ups, but getting a fix meant bringing them into the cockpit which was subject to lots of waves and spray.

All failed as a result of moisture as we had had rain and spray for two days, everything was getting damp. When it was fine, dry and sunny they all worked.

In practice you could get by with anything that floats dropped off the bow and timed till it reaches the stern.
 
Re: What\'s the point of a log?

Agree that GPS is pretty reliable and apart from a few hiccups and temporarily lost position, ours did Sterling service on our 3000 mile slowboat from Harwich into the Med. However, I would never expect to depend on it completely. It is prudent to provide other options, without going to ridiculous lengths in redundancy provision i.e. having half a dozen back ups to everything. Sailing is a sport full of uncertainty. For example, we accept that, despite very good weather forecast information, you can still get caught out. Why can't they face the prospect of equipment failure and being left without the means to navigate. I know of sailors who no longer keep up the hourly plot on the paper chart. I know of sailors who do not have a paper chart of the area in which they are sailing, relying exclusively on the GPS. "Too expensive old boy," they say. Telling them they are obliged to have a proper chart, the answer is "Who's going to know?"
Maybe the poster who started all this should junk his log and lay in a stock of suitable bits of wood so that he can work out his speed with the Dutchman's Log method. That is, unless he has woodworm on board!
 
Re: What\'s the point of a log?

If you don't use boatspeed (through the water) to watch the vessel's reaction to sail trim, which you can't if your log doesn't work, what do you use to ensure your sails are set to best effect? Only having SOG, you would never know if a change of speed was due to current or sail trim... so I think you should keep the log operational and use it. In addition when your GPS decides it has had its day, you will still have distance input for dead reckoning navigation - this being a prime reason for having a log in the first place.
 
Re: What\'s the point of a log?

Easy answer to that is to put in an imaginary waypoint along your track, and keep an eye on the ETA - sail trim affects it noticeably and it is the method I use.

Getting back to the original question - I took out my knackered old thruhull system and blanked off the hole (one less thing to worry about). I am looking out for a towed impellor, but in the meantime I have a dutchmans log which is pretty accurate - just a bit of wood and a measured length of line, followed by some simple arithmetic, can give me speed through the water to about 1/4 kn accuracy.
 
Re: What\'s the point of a log?

You can certainly sail without a log, also without any instruments at all, possibly except a steering compass and handbearing compass. I sailed for several years with just compass, estimating speed for DR plots, which you get reasonably good at with practice. You also get good at making sure you have a final good fix before the land drops out of sight on a passage, to start your DR from.

In fact the first extra nav aid beyond a compass I had was a sextant, which was most often used for vertical angles. Then came a Seafix RDF, then a Seafarer echosounder, and finally a log, mainly because logs were more expensive than the sounder or RDF.

I now sail with all the toys including a log, but as often as not it's not working properly as the paddlewheel seems to gum up with shrimps and weed every few days, and I can't be bothered cleaning it just to day-sail. I've also done several deliveries where the yacht instruments weren't working at all, so used nothing but a handheld GPS and compass.

A log is nice to have, but few are accurate, and even when you do get them calibrated accurately as I did this spring a change in the hull or paddlewheel fouling soon throws them out. Before GPS was the primary nav aid a log was reasonably high in value, but is now much less important.
 
Re: What\'s the point of a log?

It is the unreliability of the log, and the much higher reliability of the GPS that prompted the question. It's not a matter of sailing without instruments, it's a question of whether one bothers to keep and maintain an instrument that has effectively been superceded by another system. So far I've not heard any convincing argument why I should keep the thru-hull log.

There seems to be a strong GPS-sceptic theme in many of the responses but, in all probability, the US will only shut the service off when World War 3 breaks out and not knowing my speed will be the least of my problems.
 
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